Tractor

ABSTRACT

A tractor having right and left traveling crawlers ( 9 ) installed thereon, comprising a hydraulic transmission swing mechanism ( 45 ), a forced-diff ( 41 ) for driving a crawler driving sprocket ( 4 ), and an engine ( 10 ), a hydraulic transmission straight-ahead driving mechanism ( 25 ), and a transmission case ( 12 ) disposed from the front side to the rear side of a machine body in that order, wherein an allowance for heat radiation is provided to a space under a machine floor for storing the hydraulic transmission straight-ahead driving mechanism ( 25 ) to eliminate the problem of the machine floor becoming too high, and the forced-diff ( 41 ) is driven by the hydraulic transmission swing mechanism ( 45 ) with a simple structure.

FIELD OF THE INVENTION

The present invention relates to a tractor for performing agriculturalor construction work by attaching an agricultural or construction workmachine.

BACKGROUND OF THE INVENTION

In the prior art, a structure equipped with right and left hydraulictransmission mechanisms (HST) for driving right and left travelingcrawlers individually has the problem that straight-ahead travelingperformance cannot be easily improved. Another structure equipped with ahydraulic transmission straight-ahead driving mechanism for driving theright and left traveling crawlers by operating a straight-aheadtransmission lever and a hydraulic transmission swing mechanism fordriving the right and left traveling crawlers by operating a steeringwheel in order to transmit driving force of said straight-ahead drivingmechanism and said swing mechanism to the right and left travelingcrawlers through a forced-diff has the problem that, although thestraight-ahead traveling performance can be easily improved by drivingthe right and left traveling crawlers with the straight-ahead drivingmechanism, when both the hydraulic transmission swing mechanism and thehydraulic transmission straight-ahead driving mechanism are stored in aspace under a machine floor, the machine floor becomes too high toprovide space under the machine floor with an allowance for heatradiation. Another problem is that the forced-diff driven by thehydraulic transmission swing mechanism tends to become complicated, andinstallation of the swing mechanism with a heavy weight, or theforced-diff mechanism with a heavy weight, tends to result in animproper shift of the machine weight. Such additional problems of thecrawler type traveling mechanism cannot be easily constructed usingcomponents of a wheel type traveling mechanism, the installationposition of the swing mechanism is restricted, or a change in groundcontact length of the traveling crawlers tends to result in a change inswing resistance.

SUMMARIZED DISCLOSURE OF THE INVENTION

This invention relates to a tractor having right and left travelingcrawlers 9 installed thereon, comprising a hydraulic transmission swingmechanism 45, a forced-diff 41 for driving a crawler driving sprocket 4,an engine 10, a hydraulic transmission straight-ahead driving mechanism25, and a transmission case 12 disposed from the front side to the rearside of a machine body in that order, and further comprising a hydraulictransmission swing mechanism 45 disposed in the front side, wherein anallowance for heat radiation is provided to the space under the machinefloor for storing the hydraulic transmission straight-ahead drivingmechanism 25 to eliminate the problem where the machine floor becomestoo high, and the forced-diff 41 is driven by the hydraulic transmissionswing mechanism 45 with a simple structure.

In a tractor having the hydraulic transmission straight-ahead drivingmechanism 25 for driving the right and left traveling crawlers 9 byoperating a straight-ahead transmission lever 22 and the hydraulictransmission swing mechanism 45 for driving the right and left travelingcrawlers 9 by operating a steering wheel 20, wherein the driving forceof said straight-ahead driving mechanism 25 and said swing mechanism 45is transmitted to the right and left traveling crawlers 9 through theforced-diff 41, said swing mechanism 45 and said forced-diff mechanism41 are disposed of in the front lower side of the engine 10. Thereforegood longitudinal balance of the machine weight can be obtained byinstalling the swing mechanism 45 and the forced-diff mechanism 41 bothwith the heavy weight in the front lower side of the engine 10 in amachine structure having the straight-ahead driving mechanism 25 with aheavy weight and the transmission case 12 in the rear side of the engine10. A tilling work machine can be stably attached to the rear side ofthe machine body, and the difference in the ground contact pressurebetween the front side and the rear side of the traveling crawlers 9 canbe reduced to easily improve traveling performance.

The straight-ahead driving mechanism 25 and the transmission case 12 areinstalled on the rear section of the engine 10 to allow thestraight-ahead driving force of the transmission case 12 to enter theforced-diff 41 from the rear side. Thus the forced-diff mechanism 41 canbe easily mounted using front wheel driving parts that constitute awheel type traveling mechanism. Reduction of manufacturing costs can beeasily achieved by commonly using the wheel type parts, and theinstallation location can be easily changed by installing the swingmechanism 45 and the forced-diff mechanism 41 independently from thestraight-ahead mechanism 25 and the transmission case 12 in order toreduce limitation of a mounting position of the swing mechanism 45 andthe forced-diff mechanism 41.

The driving sprockets 4 and track rollers 7 for transmitting travelingforce to the traveling crawlers 9 are disposed so that the floor exitangle “A” of the traveling crawlers 9 becomes approximately 30 degreesor less. Thus the ground contact length of the traveling crawlers 9 isdetermined by the mounting position of the track rollers 7. The mountingposition of the driving sprockets can be changed longitudinally whilekeeping swing resistance almost constant. Effective ground contactlength of the traveling crawlers 9 is increased to easily securetraveling force on soft traveling surfaces that are often penetrated,and the swing resistance of the traveling crawlers 9 can be reduced toeasily improve mobility on hard surfaces that are rarely penetrated.

The transmission case 12 is installed on the rear section of the engine10 through the hydraulic transmission straight-ahead driving mechanism25. A drive shaft 43 for transmitting straight-ahead driving force tothe traveling crawlers 9 is extended forward from the transmission case12. The forced-diff mechanism 41 is installed in the forward lowersection of the engine 10. The hydraulic swing mechanism 45 fortransmitting output power of the engine 10 from the front side isinstalled in front of the forced-diff mechanism 41, and the said driveshaft 43 is connected to the rear side of the forced-diff mechanism 41from the rear side. The driving force of said swing mechanism 45 isallowed to enter from the front side of the forced-diff mechanism 41,and the right and left cases 100 are installed to both sides of theforced-diff mechanism 41 to allow the driving sprockets 4 for the rightand left crawlers 9 to be installed. Thus the longitudinal balance ofthe machine body can be easily improved because weight of heavycomponents installed on the machine body is distributed longitudinally.Simplification and manufacturing cost reduction of a drive structure ofthe traveling crawlers 9 can be easily accomplished by installing theswing mechanism 45 and the forced-diff mechanism 41 independently, sothat traveling performance and workability on farmland using thetraveling crawlers 9 can be easily improved.

The drive shaft 43 is arranged in a direction slanting horizontally fromthe longitudinal centerline of the machine body. Therefore the inputposition of the travel driving shaft 43 at the rear side of theforced-diff mechanism 41 is shifted laterally. The longitudinal width ofa casing 2 of the forced-diff mechanism 41 on which the front side ofthe swing mechanism 45 is installed in the machine body center positioncan be reduced, and simplification and size reduction of the structureof the forced-diff mechanism 41 can be easily achieved by effectivelyutilizing the lateral direction which reduces the restrictions on thedimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the tractor shown in its entirety;

FIG. 2 is a side view for explaining the machine structure;

FIG. 3 is a plain view for explaining the same;

FIG. 4 is a diagram for explaining the drive;

FIG. 5 is a diagram for explaining the steering and travel transmissionoperation;

FIG. 6 is an enlargement view of FIG. 2;

FIG. 7 is a side view of the frame section;

FIG. 8 is an enlargement view of FIG. 3;

FIG. 9 is a plain view of the frame section;

FIG. 10 is a front view of the same;

FIG. 11 is a sectional side view of the rear transmission case;

FIG. 12 is an enlargement view of the same;

FIG. 13 is a side view showing a modification of FIG. 2;

FIG. 14 is a partial enlargement view of FIG. 13;

FIG. 15 is a plain view of FIG. 13;

FIG. 16 is a partial enlargement view of FIG. 15;

FIG. 17 is an explanatory partial enlargement side view of FIG. 13;

FIG. 18 is an explanatory partial plain view of the same; and

FIG. 19 is an explanatory partial front view of the same.

THE BEST MODES EMBODYING THE INVENTION

Now some embodiments of the present invention will be described withreference to the drawings. FIG. 1 is an outline side view of thetractor, FIG. 2 is a side view of an important section, and FIG. 3 isthe plain view of the same. In this tractor, a front transmission case 2is fixed to the front section of the pair of right and left crawlerframes 1 with a square cylindrical shape. The right and left drivingsprockets 4 are supported by right and left axles 3 of the fronttransmission case 2, and the rear section of said crawler frames 1 isequipped with tension rollers 6 through tension frames 5. The travelingcrawlers 9 are wound between the drive sprockets 4, the tension rollers6 through track rollers 7 and idlers 8, and a pair of the right and lefttraveling crawlers 9 are installed.

The engine 10 is mounted on the front upper section between the rightand left crawler frames 1. The exterior of the engine 10 is covered bythe bonnet 11, and the rear transmission case 12 is installed in therear section between the right and left crawler frames 1. The hydraulicelevation cylinders 14 equipped with lift arms 13, a top link 15, and alower link 16 are installed in the rear transmission case 12, and anagricultural work machine, such as a rotary tilling work machine or aplow, is attached to links 15 and 16 in a manner permitting elevationand removal to allow for tilling work and the like on farmland.

The cabin 17 is installed on top of the rear transmission case 12 on therear side of bonnet 11. The handle column 18 and brake pedal 19 areinstalled in the front section inside cabin 17. The round type steeringwheel 20 is installed to the handle column 18 and is capable of tiltingand rotating. The driver's seat 21 is installed at the rear sectioninside cabin 17. The main and auxiliary travel transmission levers, 22and 23, and the PTO transmission lever 24 are installed on the side ofthe driver's seat 21.

As shown in FIG. 2 through FIG. 4, the front section of the reartransmission case 12 is equipped with hydraulic transmission case 25.The hydraulic transmission pump 26 for a hydraulic non-stagetransmission structure (HST) and the motor 27 are installed inside thecase 25. The pump shaft 28 for driving the pump 26 and the output shaft29 from the engine 10 are connected through the flywheel 31 inside theflywheel case 30 at the rear of the engine 10 to the damper 32 anduniversal joint shaft 33. The travel transmission output shaft 36 isconnected to the motor shaft 34 rotated by the motor 27 through the geartransmission mechanism 35 for auxiliary transmissions, and the outputshaft 36 protrudes from the rear transmission case 12 in a forwarddirection. In addition, a PTO input shaft 38 is connected to the pumpshaft 28 through a PTO clutch 37. The PTO input shaft 38 is installedalmost coaxially with the pump shaft 28. The PTO output shaft 40 isconnected to the input shaft 38 through the gear transmission mechanism39 for PTO transmission, and the output shaft 40 protrudes from the reartransmission case 12 in a backward direction to transmit power to theagricultural machine attached to the rear section of the machine body.

Right and left planetary gear mechanisms 42 forming the forced-diff 41are installed inside the front transmission case 2. The traveltransmission output shaft 36 is connected to the right and leftplanetary gear mechanisms 42 through a universal joint shaft 43 and adifferential input shaft 44 to transmit the transmission output of theoutput shaft 36 to the right and left axles 3 through the right and leftplanetary gear mechanisms 42 to drive the right and left travelingcrawlers 9 at almost the same speed in the same direction to allowforward or backward travel. The hydraulic steering case 45 is fixed onthe front face of the front transmission case 2. The hydraulic steeringpump 46 and motor 47 of the hydraulic non-stage transmission structure(HST) is installed inside the case 45, and the output shaft 29 of theengine 10 is connected to the pump shaft 48 for driving the pump 46through the universal joint shaft 49. The motor shaft 50 rotated by themotor 47 is connected to the right and left planetary gear mechanisms 42through the right and left reverse bevel gears 51 to transmit steeringoutput subjected to the non-stage transmission by the pump 46 and themotor 47 to the right and left axles 3 through the right and leftplanetary gear mechanisms 42 to drive the right and left travelingcrawlers 9 at almost the same speed in the reverse direction to allowtravel and turning to the right or the left.

As clarified above, in a tractor with the right and left travelingcrawlers 9, the hydraulic case 45 serving as a hydraulic transmissionswing mechanism, the forced-diff 41 driving the crawler drive sprockets4, the engine 10 and the hydraulic transmission case 25 serving as thehydraulic transmission straight-ahead drive mechanism, and thetransmission case 12 are disposed from the front side to the rear sideof the machine body in that order. The hydraulic steering case 45 isinstalled in the front section to provide allowance for heat radiationto the space under the machine floor for storing the hydraulictransmission straight-ahead driving mechanism 25 to eliminate theproblem of the machine floor becoming too high and to allow theforced-diff 41 to be driven by the hydraulic steering case 45 with asimple structure.

As shown in FIG. 5, the rack case 52 for steering operation output andthe steering and travel transmission operation case 53 of a tightlyclosed box type are installed. The steering wheel 20 is connected to thepinion rotating shaft 54 of the rack case 52, and the rack moving plate55 of the rack case 52 is connected to the steering operation shaft 56at the right side of the operation case 53 through the crank arm 57. Thetransmission operation input shaft 60 is connected to the maintransmission lever 22 through the link 58, and the rod 59. Thetransmission operation output shaft 64 is connected through the arm 61,and rods 62 and 63 for pump output non-stage transmission of thetransmission case 25. The steering operation output shaft 67 isconnected to the arm 65 for pump output non-stage transmission of thesteering case 45 through the rod 66 and is supported by the operationcase 53 in a rotatable manner. In addition, the transmission operationinput shaft 60 and the steering operation output shaft 67 are coaxiallyinstalled in a rotatable manner, and each of shafts 60, 64 and 67 isprotruded from the top of the case 53 and connected to the lever 22 orthe arms 61 and 65.

The connecting member 68 rotated around the shaft center by the steeringoperation shaft 56, the oscillating member 70 rotating the connectingmember 68 around the fulcrum shaft 69 from which the shaft centerintersects the operation shaft 56 almost perpendicularly, thetransmission operation input rod 71 connecting the oscillating member 70to the transmission operation input shaft 60, the transmission operationoutput rod 72 connecting the connecting member 68 to the transmissionoperation output shaft 64, and the steering operation output rod 73connecting the connecting member 68 to the steering operation outputshaft 67 are installed inside the operation case 53. The rod 73 isconnected to the connecting member 68 coaxially with the fulcrum shaft69 in a universal joint manner. The transmission operation output rod 72is connected to the connecting member 68 in a universal joint manner insuch a way that the connecting point of the transmission operationoutput rod 72 is 90 degrees apart from the connecting point of the rod73 on a circumference centered with the axis of the steering operationshaft 56, and the output shaft 64 and the rod 72 Also, the output shaft67 and the rod 73 are connected respectively in different positions onthe shaft centerline of the steering operation shaft 56.

As described above, the forced-diff 41 equipped with the right and leftplanetary gear mechanisms 42 is installed inside the front transmissioncase 2 to drive the right and left traveling crawlers 9. Thestraight-ahead traveling force is transmitted to the forced-diff 41through the travel non-stage transmission pump 26 and the motor 27 todrive the right and left traveling crawlers 9 at the same speed in thesame direction. On the other hand, swing travel force is transmitted tothe forced-diff 41 through the hydraulic steering pump 46 for swing andthe motor 47 to drive the right and left traveling crawlers 9 at thesame speed in the reverse direction. Thus outputs of both the travelnon-stage transmission pump 26 and the motor 27, and both the steeringpump 46 for swing and the motor 47 are adjusted by the steering wheel20. The travel speed is reduced in response to degree of operation ofthe steering wheel 20, and the speed difference of the right and lefttraveling crawlers 9 is continuously changed to shift to a spin-turnaction. In a condition where the main transmission lever 22 foroperating the output of the travel non-stage transmission pump 26 fortransmitting straight-ahead driving force and where the motor 27 is in aneutral position, the swing output by the steering wheel 20 is kept inthe OFF condition. When the main transmission lever 22 is operated to aposition other than neutral, the swing output of the steering wheel 20is changed in proportion to the travel transmission. Thus, when thesteering wheel 20 is in a straight-ahead position, only the travelnon-stage transmission pump 26 for transmitting straight-ahead drivingforce and the motor 27 are allowed to perform forward and backwardoutput actions in linkage with the inclination of the main transmissionlever 22. Adjustment of outputs of the steering pump 46 and the motor 47by the main transmission lever 22 is stopped. When the steering wheel 20is in a position other than straight-ahead position, adjustment of bothtravel transmission and the swing output is performed by operating themain transmission lever 22. On the other hand, both swing outputadjustment and travel transmission are performed by operating thesteering wheel 20 where the main transmission lever 22 is in a positionother than neutral.

As shown in FIGS. 2 and 3 and FIG. 6 through FIG. 10, right and leftengine frames 74 are fixed to the lower sections of both sides of theengine 10. The engine frames 74 are extended forward to fix the weight75 and the front bumper 76 on the front section. The lower middle faceof the engine frame 74 is bolted on the top of the front transmissioncase 2. The front cabin pedestals 77 for receiving and fixing the frontlower face of the cabin 17 in a detachable manner are welded to thecrawler frames 1. The right and left front cabin pedestals 77 are boltedon the right and left sides of the flywheel case 30. The rear cabinpedestals 78 for placing and fixing the rear lower face of the cabin 17in a detachable manner are welded to the rear section of the crawlerframes 1, and the right and left rear cabin pedestals 78 are bolted onthe right and left sides of the rear transmission case 12.

The front and rear section of the pair of the right and left upperframes 79 and the pair of right and left lower frames 80 are welded tothe front frame 81 and the rear frame 82 to form the frame 83. The frontframe 81 is bolted to the rear face of the flywheel case 30 in adetachable manner. The rear frame 82 is bolted to the front plate 84 ofthe rear transmission case 12 in a detachable manner. The right and leftupper frames 79 are installed on both sides in a longitudinallyextending condition at a height almost the same as that of the pumpshaft 28 and said universal joint shaft 33. The right and left lowerframes 80 are installed on both sides in a longitudinally extendingcondition at a height almost the same as that of the travel transmissionoutput shaft 36 and the universal joint shaft 43. The horizontal frame85 installed in a laterally extending condition is welded to the lowerface of the lower frame 80. The horizontal frame 85 is placed and boltedon receiver 86 of the right and left crawler frames 1 in a detachablemanner, and the middle of longitudinal width of the lower frame 80 isconnected to the crawler frames 1 through the horizontal frame 85.

As shown above, in a tractor having the traveling crawlers 9 installedin the crawler frames 1, the engine 10 and the rear transmission case 12installed in the front and rear sections of the crawler frames 1, andthe axle case 2 installed to the front section of the crawler frames 1,the frame 83 is fixed between the rear side of the engine 10 and thefront side of the rear transmission case 12, and the frame 83 isconnected to the crawler frames 1. Thus the weight and cost of theconnecting structure between the engine 10 and the rear transmissioncase 12 can be reduced, deformation of the crawler frames 1 from theweight of the machine attached to the rear section of the reartransmission case 12 can be prevented by reinforcement of the frame 83.Weight reduction, production cost reduction and strength improvement ofthe machine structure composed by said crawler frames 1 and the frame 83can be achieved.

The hydraulic transmission case 25 is fixed on the front face of thefront plate 84 of the rear transmission case 12, and the hydraulictransmission case 25 is disposed above the travel transmission outputshaft 36 between the right and left upper frames 79. The hydraulictransmission case 25 is disposed in a posture where a line connectingthe centers of the pump shaft 28 and the motor shaft 34 is inclined tothe right to reduce the vertical installation distance between the pumpshaft 28 and the motor shaft 34 in comparison with an upright posturewhere the centers of shafts 28 and 34 are arranged on the same verticalline to reduce the vertical installation distance between the pump shaft28 and the travel transmission output shaft 36, and to reduce the heightof the rear transmission case 12. In addition, the output shaft 38 andthe universal joint shaft 43 are arranged and protected over the top ofsaid horizontal frame 85. Accordingly, the hydraulic transmission case25 for transmitting output of the engine 10 to the rear transmissioncase 12 is installed inside the frame 83 to provide the frame 83 with astructure corresponding to the mounting of the hydraulic transmissioncase 25, while forming an open space sufficient for air cooling of thehydraulic transmission case 25. Therefore cooling (radiation cooling) ofthe hydraulic transmission case 25 can be easily accomplished, themounting posture of the hydraulic transmission case 25 can be freelyselected, the transmission function can be maintained, andsimplification or size reduction of the transmission structure can beachieved. By fixing the rear section of the frame 83 and the hydraulictransmission case 25 to the front plate 84 of the rear transmission case12, the machine body side of the rear transmission case 12 withdifferent specifications or conventional structure can be used only by adesign change of the front plate 84. Furthermore, the hydraulictransmission case 25 is installed to the frame 83 equipped with a traveltransmission operation mechanism with high accuracy to reducemanufacturing costs and improve handling workability, such as assemblyand disassembly.

The rack case 52 is fixed almost in parallel to the rear side of thefront frame 81 of the frame 83. The steering and travel transmissionoperation case 53 is fixed between the right and left lower frames 80.The operation case 53 is arranged at the rear side of the rack case 52to be installed inside the frame 83, and the rack case 52 and theoperation case 53 are installed by effectively utilizing the spacebetween the upper and lower power transmission universal joint shafts 33and 43. The steering and travel transmission operation case 53 isinstalled to the frame 83. The steering and travel transmissionoperation case 53 is equipped with an operation mechanism for steeringand the travel transmission is connected to the steering wheel 20 andthe main travel transmission lever 22. Thus, the operation case 53 canbe compactly stored in the frame 83 below the step of cabin 17 utilizingthe space between the rear side of the engine 10 and the front side ofthe rear transmission case 12, the handle column 18 can be made compact,and simplification and functional improvement of the steering and traveltransmission operation can be achieved by allowing steering operation tocontrol the travel transmission and the travel transmission operationthe steering control.

As shown in FIGS. 4 and 9, the brake pedal 19 installed in the cabin 17and the brake 87 installed in the front transmission case 2 areconnected through the brake link 88, brake rods 89 and 90. The brakelink 88 is supported by the fulcrum shaft 91 fixed on the right side ofthe flywheel case 30 in a rotatable manner, and the brake 87 is turnedon by pedaling the brake pedal 19 to brake the differential input shaft44. The front side of the frame 83 is fixed on the rear face of theflywheel case 30 at the rear side of the engine 10. The flywheel case 30is equipped with the fulcrum shaft 91 of a brake mechanism, the cabinmounting frame is formed on the front cabin pedestals 77 serving asconnecting frames for the crawler frames 1 and the flywheel case 30. Theengine 10 with different specifications and the frame 83 are connectedby modifying the flywheel case 30, and the disconnection and connectionof the brake pedal 19 of the cabin 17 and the brake mechanism areperformed by detaching and attaching the brake link 88 and the rod 89.Thus support strength of the engine 10, the front section of the cabin17, and the front section of the frame 83 are improved by connecting theflywheel case 30 and the crawler frames 1. Therefore, the manufacturingcost of the support section of the engine 10 can be reduced, handlingworkability such as assembly and disassembly of the cabin 17 can beimproved, and sufficient strength of the machine body such as thecrawler frames 1 and the frame 83 can be ensured.

As shown in FIGS. 11 and 12, the front plate 84 is bolted on the frontface of the rear transmission case 12 in a detachable manner, an innerwall 92 arranged almost in parallel with the front plate 84 isintegrally formed inside the rear transmission case 12 by casting, abearing plate 93 is bolted inside the rear transmission case 12 betweenthe front plate 84 and the inner wall 92 in a detachable manner, thebearing plate 93 is installed almost in parallel with the front plate84, and the bearing plate 93 is formed so as to be smaller than a frontopening of the rear transmission case 12 to allow the bearing plate 93to go in and out through the front opening of the case 12 after removingthe front plate 84.

An auxiliary transmission 1 shaft 94 and 2 shaft 95 installed in thegear transmission mechanism 35 for auxiliary transmission are supportedby the front plate 84 and the bearing plate 93 in a rotatable manner,the travel transmission output shaft 36 is supported by the bearing 96of the rear transmission case 12 and the front plate 84 in a rotatablemanner, and the transmission mechanism 35 is disposed between the frontplate 84 and the bearing plate 93 to transmit the output of the motorshaft 34 to the output shaft 36. Furthermore, the PTO input shaft 38,the PTO transmission 1 shaft 97, 2 shaft 98, and 3 shaft 99 of the geartransmission mechanism 39 for PTO transmission are supported by theinner wall 92 and the bearing plate 93 in a rotatable manner. The PTOclutch 37 connecting the PTO input shaft 38 to the pump shaft 28 isinstalled between the front plate 84 and the bearing plate 93 above thegear transmission mechanism 35 for auxiliary transmission, and the geartransmission mechanism 39 for PTO transmission is provided between theinner wall 92 and the bearing plate 93 to transmit output of the PTOinput shaft 38 to the PTO output shaft 40 through each of shafts 97, 98and 99.

As shown above, in a tractor having the front plate 84 fixed to thefront side of the transmission case 12, the bearing plate 93 installedinside the rear transmission case 12, and the hydraulic transmissioncase 25 installed on the front face of the front plate 84, the PTOclutch 37 is installed in a high position of the rear transmission case12 between the front plate 84 and the bearing plate 93, and the PTOclutch 37 is connected to the input shaft 28 of the hydraulictransmission case 25. Thus the mounting space for the PTO clutch 37 issecured above the gear transmission mechanism 35 for traveltransmission, a vertical mounting space for the gear transmissionmechanism 39 for PTO transmission and the PTO clutch 37 is reduced, andthe height of the rear transmission case 12 is reduced to make the reartransmission case 12 compact. Therefore the bearing plate 93 can beattached and detached so that the PTO input shaft 38 serving as a PTOclutch shaft is supported by the bearing plate 93. The assembly of thegear transmission mechanism 39 for PTO transmission is completed byinstalling the bearing plate 93 after mounting the gear transmissionmechanism 39 for PTO transmission on the rear transmission case 12, andthen the gear transmission mechanism 35 for travel can be installed tothe bearing plate 93 to simplify assembly procedures and facilitatedisassembly work to achieve simplification, such as for assembly anddisassembly of the transmission case 12.

The inner wall 92 integrally formed inside the rear transmission case12, the front plate 84 serving as an outer wall fixed at a side of therear transmission case 12 in a manner capable of opening and closing,and the bearing plate 93 serving as a bearing wall fixed almost inparallel between the outer wall 84 and the inner wall 92 in a detachablemanner, are installed, and the gear transmission mechanisms 39 and 35with different specifications are installed between the inner wall 92and the bearing plate 93 and between the front plate 84 and the bearingplate 93, respectively, to improve assembly workability. The reartransmission case 12 is partitioned by the bearing plate 93. The PTOgear transmission mechanism 39 is installed inside the rear section ofthe rear transmission case 12, and the travel gear transmissionmechanism 35 is installed inside the front section of the reartransmission case 12 for simplification and cost reduction of themachining of bearings inside the main body of the rear transmission case12. Thus the auxiliary transmission 1 shaft 94 can be connected to themotor shaft 34 of the hydraulic transmission case 25 in the shortestdistance. The travel transmission output shaft 36 can be protruded atthe lower section of the front plate 84 in a forward direction, thespace for installing the PTO clutch 37 can be secured above theauxiliary transmission 1 shaft 94 between the front plate 84 and thebearing plate 93, and the hydraulic transmission case 25 can beinstalled over the outer end of the auxiliary transmission 1 shaft 94 toreduce the distance between the centers of the pump shaft 34 and thetravel transmission output shaft 36.

FIG. 13 through FIG. 19 shows a modification example of the above FIG.2. As shown in FIG. 2 or FIG. 13, in a tractor having the hydraulictransmission case 25 serving as the hydraulic transmissionstraight-ahead driving mechanism for driving the right and lefttraveling crawlers 9 by operating the main travel transmission lever 22serving as a straight-ahead transmission lever, the hydraulic steeringcase 45 serving as the hydraulic transmission swing mechanism fordriving the right and left traveling crawlers 9 by operating thesteering wheel 20, and wherein driving force of the transmission case 25and the steering case 45 is transmitted to the right and left travelingcrawlers 9 through the forced-diff 41, the steering case 45 and thefront transmission case 2 with the forced-diff 41 mechanism installedtherein are disposed in the forward lower section of the engine 10, andthe transmission case 25 and the rear transmission case 12 having heavyweight are installed in the rear section of the engine 10. Thus byinstalling the steering case 45 with a heavy weight and the fronttransmission case 2 equipped with the forced-diff mechanism 41 in theforward lower section of the engine 10, a good longitudinal weightbalance of the machine body can be obtained and a tilling machine or thelike can be stably attached to the rear section of the machine bodyusing the lower link 16. The difference in load from machine body weighton the front and rear sections of the traveling crawlers 9 can bereduced to reduce the difference in ground contact pressure to improvetravel performance. The transmission case 25 and the rear transmissioncase 12 are installed in the rear section of the engine 10. Thestraight-ahead driving force of the rear transmission case 12 is allowedto enter the forced-diff 41 from the rear side, and the fronttransmission case 2 equipped with the forced-diff 41 mechanism isassembled by sharing front wheel driving parts constituting a wheel typetravel mechanism such as, for example, the axle 3, its mounting parts,and transmission parts to reduce manufacturing costs by commonly usingparts of the wheel type. In addition, the steering case 45 and the fronttransmission case 2 equipped with the forced-diff 41 mechanism areinstalled independently from the transmission case 25 and the reartransmission case 12 to minimize limitation of mounting positions of thesteering case 45 and the front transmission case 2 equipped with theforced-diff 41 mechanism to allow an installation location to be easilychanged.

As shown in FIG. 13, the driving sprockets 4 for transmitting travelingforce to the traveling crawlers 9, and the equalizer wheels 7 serving astrack rollers, are installed in where the floor exit angle “A” of thetraveling crawler 9 becomes approximately 30 degrees or less. Groundcontact length of the traveling crawlers 9 is determined by adjustingthe mounting position of a foremost equalizer wheel 7 close to thedriving sprocket 4, and the mounting position of the driving sprocket islongitudinally changed while keeping swing resistance almost constant.Thus effective ground contact length is increased by ground contact ofthe front section of the traveling crawlers 9 with a floor exit angle“A” of 30 degrees or less on a soft surface requiring deeper penetrationto secure traveling force. The ground contact length is decreased by thefloor exiting the front section of the traveling crawlers 9 on a hardsurface requiring less penetration to reduce the swing resistance toimprove mobility.

The rear transmission case 12 is installed in the rear section of theengine 10 through the hydraulic transmission type transmission case 25,and the universal joint shaft 43 serving as a travel drive shaft fortransmitting straight-ahead driving force to the traveling crawlers 9 isextended forward from the transmission case 12. The front transmissioncase 2 equipped with the forced-diff 41 mechanism is installed in theforward lower section of the engine 10, hydraulic transmission steeringcase 45 for transmitting output of the engine 10 from the front side isinstalled to the front side of the front transmission case 2 equippedwith the forced-diff 41 mechanism, the universal joint shaft 43 isconnected to the rear side of the front transmission case 2 equippedwith the forced-diff 41 mechanism from the rear side, driving force ofthe steering case 45 is allowed to enter from the front side of thefront transmission case 2 equipped with the forced-diff 41 mechanism,right and left final cases 100 are installed to both sides of the fronttransmission case 2 equipped with the forced-diff 41 mechanism, and thedriving sprockets 4 for the right and left traveling crawlers 9 areinstalled in the final cases 100 through the axles 3. Thus componentswith heavy weight disposed in the machine body are longitudinallydistributed to improve longitudinal balance of the machine body, and thesteering case 45 and the front transmission case 2 equipped with theforced-diff 41 mechanism are installed independently from thetransmission case 25 and the rear transmission case 12 to simplify thedrive structure of the traveling crawlers 9, reduce the manufacturingcosts, and improve the travel performance using the traveling crawlers 9and the workability on a farmland.

The universal joint shaft 43 is extended in a manner horizontallyslanted from the longitudinal centerline of the machine body, theconnecting section of a bevel gear 101 of the differential input shaft44 is arranged to the left side of a connecting section of the bevelgear 51 of the motor shaft 50 as shown in FIG. 18, and the differentialinput shaft 44 in an input position of the universal joint shaft 43 atthe rear side of the front transmission case 2 equipped with theforced-diff 41 mechanism is shifted to the left to minimize longitudinalwidth of the front transmission case 2 serving as a casing of theforced-diff 41 mechanism equipped with the steering case 45 at the frontside in a position of a machine body center to effectively utilize thelateral mounting space of the front transmission case 2 with less sizelimitations to simplify or reduce the size of the front transmissioncase 2 structure equipped with the forced-diff mechanism 41.

As shown in FIG. 13 through FIG. 16, the right and left front cabinpedestals 77 and the rear cabin pedestals 78 are connected through theright and left side frames 102 to reinforce support strength of thecabin 17 of the crawler frames 1 connected to each of the cabinpedestals 77 and 78 by installing the side frames 102. The steering case45 is fixed to the front side of the front transmission case 2 throughthe gear case 103, the steering input shaft 104 connected to the pumpshaft 48 through gears is protruded from the upper rear face of the gearcase 103, the steering input shaft 104 is connected to the output shaft29 of the engine 10 through the universal joint shaft 49, the steeringcase 45 is installed in a position lower than that of the output shaft29 in front of the engine 10, and the cooling parts, such as a radiatorand an oil cooler, are installed inside the bonnet 11 above the steeringcase 45.

The front PTO shaft 105 is formed by protruding the pump shaft 48 to theforward side of the steering case 45, the pulley 106 for V-belts isinstalled to the front PTO shaft 105 if necessary, and when a machine,such as a fertilizer sprinkling machine, is attached to the front bumper76, work power is derived from the front PTO shaft 105. Thus both sidesof the steering case 45 are protected by the right and left engineframes 74, the bottom face of the steering case 45 is protected by thebottom bumper 107 as shown in FIG. 14, and reinforcing frames 108 areinstalled outside the engine frames 74 as shown in FIG. 16 to increasethe strength of the right and left front cabin pedestals 77 forsupporting the engine 10 by the right and left reinforcing frames 108.

1. A tractor comprising: an engine; a hydraulic transmission swingmechanism and a hydraulic transmission straight-ahead driving mechanismdriven by said engine, said straight-ahead transmission having atransmission case; a forced-diff for combining output of said swingtransmission and said straight-ahead transmission; right and lefttraveling crawlers driven by said forced-diff; a first connecting unitcomprising said swing transmission and said forced-diff, wherein saidfirst connecting unit is installed forward of said engine andlongitudinally spaced from said engine by a first predetermineddistance; a second connecting unit comprising said straight-aheadtransmission and said transmission case, wherein said second connectingunit is installed rearward of said engine and longitudinally spaced fromsaid engine by a second predetermined distance; and a machine floorinstalled between said engine and said second connection unit.
 2. Thetractor of claim 1, having right and left driving sprockets, whereinsaid first connection unit is disposed between said right and leftsprockets.
 3. The tractor of claim 1 or 2, having a longitudinalcenterline and a width, said tractor further comprising: a traveldriving shaft for outputting straight-ahead driving force to saidforced-diff, said shaft extending forward from said transmission case sothat, in a plan view, said shaft slants away from said longitudinalcenterline; and a first input position defined by a line between saidswing transmission and said forced-diff, and a second input positiondefined by a line between said straight-ahead transmission and saidforced-diff, wherein said first and second input positions are offsetfrom each other with respect to said tractor width.